片段:找不到活动?

Question

所以我正在尝试通过单击默认模板导航栏上的按钮来启动片段，我正在使用片段事务并提交，但应用程序崩溃，无法找到隐藏在下拉菜单上的 android 监视器错误部分中的活动。我使用替换和添加时遇到此崩溃。

这是我试图添加的片段：

public class FoodScroll extends ListFragment implements AdapterView.OnItemClickListener{
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
return inflater.inflate(R.layout.fragment_foodscroll, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
ArrayAdapter adapter = ArrayAdapter.createFromResource(getActivity(), R.array.foods, android.R.layout.simple_list_item_1);
setListAdapter(adapter);
getListView().setOnItemClickListener(this);
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id){
Toast.makeText(getActivity(), "Item" + position, Toast.LENGTH_SHORT).show();
}
}

这是我尝试将其放入的活动：

public class MainActivity extends AppCompatActivity{
private FragmentManager manager = getFragmentManager();
private FragmentTransaction transaction = manager.beginTransaction();
private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
= new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.navigation_home:
FoodScroll foods = new FoodScroll();
transaction.replace(R.id.container, foods);
transaction.commit();
return true;
case R.id.navigation_dashboard:
return true;
case R.id.navigation_notifications:
return true;
}
return false;
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
}
}

包语句没有丢失，我把它从代码段中取出。 如果我错误地放置了代码或其他东西，请道歉。

logcat无法正常工作，我不得不重新启动android工作室才能使其再次工作。这就是显示的内容

03-15 22:57:17.090 3238-3238/? I/art: Not late-enabling -Xcheck:jni (already on)
03-15 22:57:17.090 3238-3238/? W/art: Unexpected CPU variant for X86 using defaults: x86
03-15 22:57:17.110 3238-3245/? E/art: Failed sending reply to debugger: Broken pipe
03-15 22:57:17.110 3238-3245/? I/art: Debugger is no longer active
03-15 22:57:17.110 3238-3245/? I/art: Starting a blocking GC Instrumentation
03-15 22:57:17.199 3238-3238/? W/System: ClassLoader referenced unknown path: /data/app/com.namename.www.name-2/lib/x86
03-15 22:57:17.253 3238-3238/? W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
03-15 22:57:17.393 3238-3238/? I/InstantRun: Starting Instant Run Server for com.namename.www.name
03-15 22:57:17.454 3238-3262/? I/OpenGLRenderer: Initialized EGL, version 1.4
03-15 22:57:17.454 3238-3262/? D/OpenGLRenderer: Swap behavior 1
03-15 22:57:17.454 3238-3262/? W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
03-15 22:57:17.454 3238-3262/? D/OpenGLRenderer: Swap behavior 0
03-15 22:57:17.488 3238-3238/? W/art: Before Android 4.1, method int android.support.v7.widget.ListViewCompat.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
03-15 22:57:25.564 3238-3238/com.chilosomexicanbistro.www.chiloso D/AndroidRuntime: Shutting down VM
03-15 22:57:25.564 3238-3238/com.chilosomexicanbistro.www.chiloso E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.namename.www.name, PID: 3238
              java.lang.RuntimeException: Content has view with id attribute 'android.R.id.list' that is not a ListView class
                  at android.app.ListFragment.ensureList(ListFragment.java:402)
                  at android.app.ListFragment.onViewCreated(ListFragment.java:203)
                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1010)
                  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1171)
                  at android.app.BackStackRecord.run(BackStackRecord.java:816)
                  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578)
                  at android.app.FragmentManagerImpl$1.run(FragmentManager.java:483)
                  at android.os.Handler.handleCallback(Handler.java:751)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6119)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

这里有几个问题：

问题 1 - 错误地使用静态初始化

private FragmentManager manager = getFragmentManager(); //no! don't do this
private FragmentTransaction transaction = manager.beginTransaction(); //no!

使用静态初始化不适用于 Android 活动生命周期。请仔细研究这些内容，并密切关注 Android 文档中的示例 - 您几乎不会在示例活动和片段中找到任何静态初始化。

问题 2 - 不检查片段管理器以查看它是否已包含片段

switch (item.getItemId()) {
case R.id.navigation_home:
FoodScroll foods = new FoodScroll(); //no! check first if the fragment is already in the FragmentManager
transaction.replace(R.id.container, foods);
transaction.commit();
return true;

这段代码是错误的 - 同样，在示例中，您几乎总是看到按习惯编写的调用getFragmentManager().beginTransaction()...。请尝试更仔细地遵循文档中的示例片段和活动。相信我，它会节省您的时间:)

而不是上面的代码，我认为你想要这样的东西：

case R.id.navigation_home:
FoodScroll foods = getFragmentManager().findFragmentByTag("FOOD");
if (foods == null) {
foods = new FoodScroll();
}
getFragmentManager().beginTransaction().replace(R.id.container, foods, "FOOD").commit();
return true;

问题 3 - 使用正确的堆栈跟踪进行 OP 编辑后更新：

根据Mike M的评论，在ListFragment中，如果使用自己的布局，ListView的ID必须是@android:id/list的。